The enzyme aryl sulfatase A is critically important in the genetic disease metachromatic leukodystrophy and may also play a role in the hydrolysis and inactivation of certain carcinogenic intermediates, the metabolism of ascorbic acid derivatives, and the metabolism of steroid derivatives. The kinetic behavior, structure and mechanism of action of rabbit liver aryl sulfatase A (G.D. Lee and R.L. VanEtten, Arch. Biochem. Biophys., 166, 280-294 (1975)) will be studied in an effort to understand the molecular basis of its anomalous kinetic behavior - the progressive and rapid inactivation of the enzyme which occurs as it hydrolyzes substrate. The nature of the turnover-modified enzyme will be examined for structural changes and for the presence of bound substrate or inhibitor molecules. The subunit structure of the enzyme and its reversible association-dissociation interactions will be studied under varied conditions. The possible relationship of the subunit structure of the enzyme to its anomalous kinetic behavior will be studied. Studies on the reactions of the enzyme with covalent modification reagents including diethyl pyrocarbonate will be extended.